1. Field of the Invention
The present invention relates to a phase shift full bridge power converting system and a control method thereof, and more particularly, to a control method which switches states according to an output load state to optimize the performance of the power supply.
2. Description of the Prior Art
As global warming becomes a major concern, there have been studies on how to improve the efficiency of the power converters to reduce the CO2 emission. It is estimated that in average family has 20 appliances which consume power while they are not in operation. The power consumed is about 5% to 10% of the total power used for one family. This power consumption is used for keeping the appliances in standby states and for the power converters to converting AC power to DC power. Therefore, it is necessary to reduce the power consumption of the power converter while it is in the standby mode.
There are different power supply designs, such as a single-stage or a multi-stage power supply design for power converters operating in different load conditions. The single-stage power supply is often applied for low wattage equipment. Common low wattage single stage power converters comprise fly back type, forward type and half bridge type single stage power converters. On the other hand, the multi-stage power supply is often applied for high wattage equipment for there could be a low power factor problem. The first stage of the multi-stage power supply is an AC/DC power factor corrector for improving the power factor to be as close as a unity power factor and the second stage is a phase shift full bridge DC/DC power converter for providing a highly efficient and stable DC voltage. During the standby state, the first stage will stop switching, but the second stage keeps operating for supplying a stable DC voltage to the load, and therefore, most of the standby power consumption is from the second stage phase shift full bridge DC/DC power converter. Besides, the phase shift full bridge DC/DC power converter still cannot achieve zero voltage switching under a light load condition and causes additional power consumption during the light load state.
Therefore, the prior art power converting techniques present several shortcomings to be overcome.
In view of the deficiencies of the prior art power converting techniques, after years of constant researches, the inventor has successfully proposed a phase shift full bridge power converting system and a control method thereof in the present invention.